Bitumen based materials which include hot bitumen binders, the residues obtained from cut back bitumen, and bitumen emulsions are widely used in road and building constructions and coatings. The strong adhesion and film formation properties make them ideal materials for pavement building, repairing, maintenance and preservation, protective coatings, and water proofing coatings. For example, tack coats by hot applied asphalt binder or spray (cold or warm) applied asphalt emulsion is often used to provide a thin adhesive film of asphalt between the existing pavement and a new surface layer. The formed tack or bond coats reduce the risk of slippage between the two layers. Good contact without slippage allows the stress in the pavement to be uniformly distributed. Bituminous materials are also widely used in fog seal, primes, crack filling, and sealing. Fog seal is a light spray application of asphalt emulsion primarily onto existing asphalt surfaces to seal minor cracks, reduce raveling, and enrich dry and worn out pavements. Prime coats of conventional asphalt emulsion can be used to provide a water resistant membrane of asphalt to seal road bases, sub-bases and sub-grades and to prevent ingress of water or water loss by surface evaporation, to control dust, and to provide a good surface for subsequent paving or sealing operations. Prime coats also ensure good bonding of a bituminous overlay. Protective coatings based on bituminous materials are applied to metal castings or pipework. Waterproofing coatings are applied to building envelope, water retention ponds, pipes, etc.
One drawback of bitumen based materials is that they are tacky and have a tendency to transfer to surfaces that come in contact with them. For example, bitumen applied to a roadway may be picked up by the tires of passing traffic or construction equipment, especially at elevated temperatures. For tack coat applications, when pick up occurs, it can damage the bituminous film and hence reduce the bond between the layers. Bitumen picked up by the tires would then be deposited (“tracked”) on adjacent roads which could cause safety issues and increase clean-up costs to paving contractors. In the case of bitumen coated metal goods, they may stick to each other during storage or handling leading to damage to the coating.
It is known that very hard bitumen materials with high softening point are much less sticky. Non-tracking tack coats have been developed to minimize pick up of the binder by the tires of traffic or construction vehicles. These trackless tack coats are prepared from hard asphalt binder, generally with a softening point above 65° C. and a penetration less than 40 dmm, and applied as hot liquid or in emulsion form. The bitumen materials could be low penetration asphalts available from the refining of crude oil, oxidized bitumen and blends of these materials with softer bitumen (>40 pen), or produced by blending softer grade bitumen with modifiers such as Gilsonite, polymers, high melting point waxes, or minerals. Alternatively, emulsions of soft bitumen could be blended with water dispersions or emulsions of the modifiers, and when the emulsion mixture dries the resulting residue has the desired non tacky, non-tracking properties. Similar modifications to asphalt binders and asphalt emulsions discussed above are also utilized to make non-tracking bitumen for use as primes and fog seals or to prepare protective or waterproofing coatings to construction materials, metal castings, etc.
However, hard asphalt binders with low penetration are not abundantly available and the need for non-sticky character may adversely affect other properties such as ductility at low temperature, resistance to cracking or aging. In many cases such as in tack and prime applications, the desired non-tracking properties need only be temporary, since eventually the tack or prime is covered by an asphalt layer and is not exposed to traffic.
U.S. Pat. No. 6,025,016 relates to a binder layer composed of a primary binder film such as a tack coat, a seal coat, or a binder membrane, covered with an aqueous protective composition, which can be driven over. The aqueous protective layer can contain inorganic or organic fillers.
FR 2025771 relates to the use of aqueous dispersions containing bituminous substances and minerals that swell as spray agents for the surface treatment of bituminous traffic surfaces.
The formulation of storage-stable emulsions from hard asphalts or containing additives such as minerals and waxes designed to give non-tracking character to the residue may be technically challenging, and it is especially difficult to combine fast curing emulsion with storage stability.